The objective of the invention is continuous temperature monitoring of refrigerated and--especially--frozen products, which are perishable--even during short-term defrosting.
Methods are known using an indicator, in which one or more liquids with varying melting points are encapsuled, for instance -18.degree. C., -8.degree. C. and 0.degree. C. (-0.4.degree. F., 17.6.degree. F. and 32.degree. F. resp.). The indicator is being frozen prior to being added to the product to be monitored. In order to recognize possible melting of the liquids they are first brought into a certain geometric pattern which they lose in case melting occurs. A known method uses centrifugation of the indicator during the freezing process. Thus the liquid is being propelled into the outermost areas of the cavities where it is frozen. In case one of the melting temperatures is exceeded, the respective liquid starts to run and assumes a different shape. Even in case of renewed freezing the liquid never regains the original geometric pattern resulting from the centrifugation.
FIG. 1 and FIG. 2 indicate the functioning of such known procedure. FIG. 1 shows an indicator 8 with three "eyes" 1, 2 and 3 prior to centrifugation and freezing. FIG. 2 shows the identical indicator following centrifugation and freezing.
The objective of this invention is to avoid the complicated process of centrifugation.